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mapStateToProps is not always called synchronously

See original GitHub issue

found a very hard to trace bug in my app and it seems like mapStateToProps is not being called the same. I’m able to replicate the behaviour in codesandbox

https://codesandbox.io/s/m075w1wq8

AppContainer is the parent AppContainer2 is the child

before dispatch
parent mapStateToProps 1
after dispatch
child mapStateToProps 1

check the console.log and found that parent’s mapStateToProps is being called synchronously, which is within the dispatch call, but the child’s mapStateToProps is being called after dispatch call

I think this is because the subscription in the connect function is trying to defer it after componentDidUpdate in the parent

please close this if this is intended

Issue Analytics

State:
Created 5 years ago
Reactions:1
Comments:12 (5 by maintainers)

Top GitHub Comments

1reaction

markeriksoncommented, Jun 28, 2021

The dispatches themselves are synchronous. The re-rendering of the UI is batched.

This issue really isn’t a good place to provide support. If you’re having problems, the best option is to ask in either Stack Overflow or Reactiflux, and provide a CodeSandbox or repo that demonstrates whatever problem you’re seeing, rather than sort of poking around at implementation details.

1reaction

markeriksoncommented, Jun 28, 2021

See my other post A (Mostly) Complete Guide to React Rendering Behavior for details on how React batching works.

The other factor is that React-Redux v7 also uses batching internally.